Similar to the sexual term, it generally means to have somebody in a favorable position, like after beating the shit out of them, and ramming any object of your choice into one of their main orifices, like their mouth or anus.
However, many people don't know how to taste with their anus, so you might as well just say it in a foreign language, like:
smak tęczy, BITCH
OR
die smaak van die reënboog, BITCH
Mr. Maynard hid in the bathroom stall, waiting for Mr. Concubine, where he proceeded to rip his genitalia off and beat him with it. He then whipped out his OWN dinosaur penis with flaming coconuts and forcefully rammed it into Concubine's orifice while saying "TASTE THE RAINBOW, BITCH!!!!"
The act of putting skittles into some unlikely body part for the purposes of feeding another. See pez dispenser, orbit gumming.
Sean: How's it going there, Jess?
Jess: Mmmmpph Mmph!
Sean: Pull your head out for a second. I can't understand a word you're saying.
***Thwwwp***
Jess: I taste it! I taste it! I taste the rainbow! (She looks up at Sean with a speckled smile).
Sean: (Disgusted) Ok, back to work. (Closes his eyas and leans in).